1. Field of the Invention
The present invention relates to a display device and, more particularly, to an improvement in a liquid crystal display device having an electroluminescence (to be referred to as an EL hereinafter) panel as a backlight source.
2. Description of the Prior Art
An EL panel is conventionally utilized as a backlight source for a liquid crystal display device. When an EL panel is used as a backlight source, the circuit portions of the display device mounted on the circuit board must be protected from electromagnetic wave noise generated by the EL panel.
In a liquid crystal display device disclosed in Japanese Unexamined Patent Publication No. 9-152605, as shown in FIG. 1, an EL panel 52 is placed on a circuit board 51 by stacking, a liquid crystal panel 54 is placed on an emission surface 52a side of the EL panel 52 by stacking, and a frame 55 is mounted on the surface of the liquid crystal panel 54. A shield layer 53 is formed on the lower surface of the EL panel 52. Since the shield layer 53 is provided between the EL panel 52 and circuit board 51, the electromagnetic wave noise generated by the EL panel 52 is prevented from adversely affecting the respective circuits on the circuit board 51.
In the liquid crystal display device of this type, the electromagnetic wave noise generated by the EL panel can be prevented from adversely affecting the respective circuits on the circuit board. If, however, the liquid crystal display device is applied to a portable terminal such as a cellular phone or PHS, since a display 33 is arranged near an ear piece 32, as shown in FIG. 2, the acoustic noise generated by the EL panel increases due to the resonance of the display 33. Even slight noise becomes offensive to the ear to discomfort the user.
The present invention has been made in consideration of the above situation of the prior art, and has its object to provide a liquid crystal display device in which noise output from a speech reception port and a display due to acoustic noise from an EL panel can be decreased.
In order to achieve the above object, according to the first main aspect of the present invention, there is provided a liquid crystal display device comprising a shield layer for acoustic noise prevention between an LCD and an EL panel serving as a backlight source for the LCD.
In addition to the first main aspect, the present invention also has auxiliary aspects as follows.
According to the first auxiliary aspect, the shield layer of the first main aspect is fixed to a surface of the EL panel by adhesion.
According to the second auxiliary aspect, the shield layer of the first main aspect is fixed to the LCD through a double-coated tape by adhesion.
According to the third auxiliary aspect, the shield layer of the first main aspect is a transparent electrode layer connected to ground.
According to the fourth auxiliary aspect, the transparent electrode layer of the third auxiliary aspect is formed on one entire surface of the EL panel.
According to the fifth auxiliary aspect, the transparent electrode layer of the third auxiliary aspect has an impedance set to less than several ten kxcexa9.
According to the sixth auxiliary aspect, the shield layer of the first main aspect is a conductor selected from a group consisting of an ITO foil, an aluminum foil and silver foil.
In order to achieve the above object, according to the second main aspect of the present invention, there is provided a liquid crystal display device comprising a ground plate between an LCD and an EL panel serving as a backlight source for the LCD.
The ground plate of the second main aspect is formed by forming a transparent electrode layer on one surface of a PET film.
According to the present invention having the aspects described above, an electromagnetic wave preventive ground plate having a transparent electrode layer or transparent electrode connected to ground is placed between an LCD and an EL panel to shield an electric field that varies in accordance with a drive frequency generated by the EL panel. Resonance (acoustic noise) between the EL panel and the transparent electrode of the LCD can accordingly be decreased. As a result, noise output from the ear piece and display can be decreased.